[Bug rtl-optimization/64990] New: wrong code at -O1, -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64990

            Bug ID: 64990
           Summary: wrong code at -O1, -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -O1,
-O2 and -O3 in both 32-bit and 64-bit modes. 

It also affects 4.6.x through 4.9.x. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/5.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 5.0.0 20150209 (experimental) [trunk revision 220527] (GCC) 
$ 
$ gcc-trunk -O0 small.c; a.out
$    
$ gcc-trunk -O1 small.c
$ ./a.out
Segmentation fault (core dumped)
$ 



--------------------------



static int a = 770, c, f;
int b, d, e = 1, h, i, j;

static int
fn1 ()
{
  int g[1];
  c = 0;
  for (;;)
    {
      if (e)
    break;
      return g[(a + 1) * 6 + (f + 1) * 3 + 1];
    }
  if (b)
    return d;
  return 0;
}

int
main ()
{
  h = fn1 ();
  if (j)
    i = 0;
  return 0;
}